WO2009038865A1

WO2009038865A1 - Method for obtaining biodiesel, alternative fuels and renewable fuels tax credits and treatment

Info

Publication number: WO2009038865A1
Application number: PCT/US2008/070183
Authority: WO
Inventors: William Douglas Morgan
Original assignee: Endicott Biofuels Ii, Llc
Priority date: 2007-09-19
Filing date: 2008-07-16
Publication date: 2009-03-26
Also published as: US20090076913A1

Abstract

The present invention relates to a method of obtaining U.S. Federal and State tax credits, U.S. Federal renewable fuel treatment, and other incentives by production of esters manufactured by the esterification of carboxylic acids using slurry phase, heterogeneous catalyzed, reactive distillation, and sale thereof for U.S. consumption as a renewable fuel.

Description

Method for Obtaining Biodiesel, Alternative Fuels and Renewable Fuels Tax Credits and Treatment

This application claims priority under 35 U. S. C. 119(e) to U.S. provisional application 60/973,726, filed September 19, 2007, the contents of which are incorporated by reference in their entirety.

Field of Invention

Background

Diesel fuel is a refined petroleum product which is burned in the engines powering most of the world's trains, ships, and large trucks. Petroleum is a non-renewable resource of finite supply. Acute shortages and dramatic price increases in petroleum and the refined products derived from petroleum have been suffered by industrialized countries during the past quarter-century. Furthermore, diesel engines which run on petroleum based diesel emit relatively high levels of certain pollutants, especially particulates. Accordingly, research effort is now being directed toward replacing some or all petroleum-based diesel fuel with a cleaner-burning fuel derived from renewable sources such as farm crops, agricultural waste streams or municipal or other waste streams.

In an effort to partially replace dependence on petroleum-based diesel, vegetable oils have been directly added to diesel fuel. These vegetable oils are composed mainly of triglycerides, and often contain small amounts (typically between 1 and 10% by weight) of free fatty acids. Some vegetable oils may also contain small amounts (typically less than a few percent by weight) of mono- and di-glycerides.

Triglycerides are esters of glycerol, CH₂(OH)CH(OH)CH₂(OH), and three fatty acids. Fatty acids are, in turn, aliphatic compounds containing 4 to 24 carbon atoms and having a terminal carboxyl group. Diglycerides are esters of glycerol and two fatty acids, and monoglycerides are esters of glycerol and one fatty acid. Naturally occurring fatty acids, with only minor exceptions, have an even number of carbon atoms and, if any unsaturation is present, the first double bond is generally located between the ninth and tenth carbon atoms. The characteristics of the triglyceride are influenced by the nature of their fatty acid residues.

The production of alkyl esters from glycerides by transesterification is a known process. However, transesterification suffers in that the reaction generally requires the addition of an acid or base catalyst which must be neutralized after the reaction, thereby generating salts and soaps. In addition, while transesterification results in the separation of fatty acid esters from triglycerides, it also results in the production of glycerin, which must then be separated from the fatty acid esters, excess alcohol, salts, and soaps. Furthermore, the use of a strong acid, such as sulfuric acid, typically leads to higher sulfur content in the resulting biodiesel as the acid reacts with the double bonds in the fatty acid chains.

In an effort to overcome some of the problems associated with transesterification, several attempts have been made to employ esterification between fatty acids and alcohols. In these processes fatty acids are prepared from triglycerides by hydrolysis, followed by catalyzed esterification of the fatty acids with an alcohol, preferably methanol. While this procedure is practiced in the production of fatty alcohols and fatty acid esters, as described in U.S. Pat. No. 5,536,856 (Harrison et al), it has not been practiced in the production of biodiesel fuel. Despite any research that may now be directed toward replacing some or all petroleum-based diesel fuel with a cleaner-burning fuel derived from a renewable source such as farm crops, processes for producing renewable fuels as an alternative to petroleum products have not had economic success. As a result, both federal and state governments in the United States have created economic incentives for alternative fuels. However, for any original process in development, there may be no information as to the incentives and credits for which the process may be eligible. Thus, there is a need for methods of obtaining economic incentives and tax credits for original processes, particularly in relation to the alternative fuel industry.

Summary of Invention

The present invention provides for the use of heterogeneous, slurry phase, reactive distillation to convert carboxylic acids to esters. In a preferred embodiment, the present invention employs reactive distillation as a method to assist in the production of biodiesel fuel having low glycerin, water and sulfur content. Reactive distillation is a method wherein specific reactions are driven forward despite an unfavorable equilibrium position for the main reaction, where the driving force during the reaction is the continuous removal of one or more substances from the reaction mixture. By removal of one or more products, the reaction equilibrium may become favorable. Sulfur content is reduced by employing reactive distillation over a solid catalyst bed and free glycerin concentration is reduced by employing fat hydrolysis.

While the present invention is a technical advance over the prior art, various marketplace factors may interfere with the widespread adoption of the present invention. Therefore, the present invention also provides methods for obtaining Federal and State Tax Credits and other incentives for the production of biodiesel and alternative ester-based fuels. In a preferred embodiment, the disclosed process for production of ester-based fuels is coupled with the methods of obtaining credits and incentives in order to provide cost advantages over the prior art.

According to one aspect of the present invention, carboxylic acids suitable for further conversion to fuel esters, the use of which can further generate tax credits and other incentives, are obtained by hydrolysis of glycerides, by distillation from mixtures of fatty acids and glycerides, or by acidulation of carboxylic acid soaps. The fatty acids are then transformed to biodiesel by reaction of a fatty acid component and an alcohol component, in which the fatty acid component and alcohol component are passed in countercurrent relation through an esterifϊcation zone maintained under esterification conditions and containing a solid esterifϊcation catalyst. In certain embodiments, the esterifϊcation catalyst may be selected from particulate ion exchange resins having sulfonic acid groups, carboxylic acid groups or both. The process is characterized in that the esterifϊcation zone includes a column reactor provided with a plurality of esterifϊcation trays mounted one above another, each adapted to hold a predetermined liquid volume and a charge of solid esterifϊcation catalyst. The less volatile component of the fatty acid component and of the alcohol component is supplied in liquid phase to the uppermost section of the reaction column and the more volatile component is supplied as a vapor to a lower portion of the reaction column. Vapor comprising the more volatile component and water from the esterifϊcation can be recovered from an upper part of the column reactor, and the biodiesel can be recovered from a lower part of the column reactor.

In another embodiment, a process for the preparation of biodiesel from a fatty acid feedstock is provided. A methanol vapor feedstream and a fatty acid feedstream are continuously introduced to a reaction vessel. The methanol and fatty acid are catalytically reacted in a reaction zone in the presence of a heterogeneous esterifϊcation catalyst within the reaction vessel to produce fatty acid methyl esters and water. The water is removed from the reaction zone with the methanol vapor and is separated from the alcohol, and the biodiesel is collected as the bottoms product.

In another embodiment, a process for preparing a biodiesel fuel from a triglyceride feedstock, wherein the biodiesel has a low glycerin and sulfur content is provided. The triglyceride feedstock is introduced into a fat splitter to produce a fatty acid-rich feedstream, which can be continuously fed to a reaction vessel. Similarly, an alcohol vapor feedstream is introduced to the reaction column. The fatty acid feedstream and alcohol feedstream catalytically react as they pass countercurrently among the equilibrium stages that hold a solid catalyst to produce biodiesel and water. Water is stripped from the reaction vessel along with alcohol vapor due to the action of the equilibrium stages, separated from the alcohol in an additional step and the alcohol is recycled to the reaction vessel. In one embodiment, the catalytic zone includes an ion exchange resin catalyst comprising -SO₃H or -CO₂H functional groups.

In another embodiment, a biodiesel fuel is prepared having water content less than 0.050% by volume. In another embodiment, the biodiesel fuel has a kinematic viscosity that is between 1.9 and 6 mm²/s. In another embodiment, the biodiesel fuel has a sulfur content that is less than 500 ppm, preferably less than 15 ppm. In another embodiment, the free glycerin content of the biodiesel fuel is less than 0.020% by weight. In another embodiment, the total glycerin content of the biodiesel is less than 0.240% by weight.

In another embodiment, biodiesel prepared by the methods of this invention are further employed to obtain tax credits, production incentives, renewable fuel treatment or all three. In one embodiment, esters that meet IRCs definition of Agri-Biodiesel are prepared from fatty acids according to the methods of the invention. These esters are then blended with 0.1 to 99.9% taxable diesel (as defined by IRC) prior to sale to a third party for use as or used by the producing taxpayer for fuel. In doing this, $1.00 per gallon in refundable tax credits under IRC Section 6426 are obtained from the Federal Government, if available. Depending on the state where the material is produced, state incentives are also obtained.

In another embodiment, esters meeting IRCs definition of biodiesel are produced, blended according to 6426 rules, and then sold to a third party for use as or used by the producing taxpayer for fuel and $0.50 per gallon in refundable Federal tax credits are obtained, if available. Depending on the state where material is produced, state incentives are also obtained.

In another embodiment, esters that fail to meet IRCs definition of Agri-biodiesel or biodiesel but which meet ASTM specifications for other fuels are blended with taxable fuel and sold for use as a fuel or used by the producing taxpayer in order to generate $0.50 in refundable Federal tax credits under Section 6426, if available, along with any additional state incentives.

In another embodiment, application is made to EPA for registration of esters that otherwise fail to meet IRCs definition of Agri-biodiesel or biodiesel but which meet ASTM specifications for other fuels. Once registration is obtained, these non-biodiesel esters are blended with taxable fuel and sold for use as a fuel or used by the producing taxpayer in order to generate $1.00 in non-refundable Federal tax credits under Section 4OA, if available, along with any additional state incentives.

In another embodiment, the producers maintain qualification as a small agri-biodiesel producer such that the methods of the invention permit claiming of small agri-biodiesel producer credits from the federal government.

In another embodiment of the invention, esters meeting the definition of biodiesel and/or Agri-biodiesel are used by the taxpaying producer or placed directly in the fuel tank of a user at retail without blending with other taxable fuel. In doing so, non-refundable Federal Tax credits of $0.50 for biodiesel and/or $1.00 per gallon for Agri-biodiesel are generated under Section 4OA, if available, along with any applicable state credits and/or incentives.

In another embodiment of the invention, by-products from the method of the invention such as distillation bottoms are blended with taxable fuel and sold to third parties for use as or used by the producing taxpayer as fuel. In doing so, $0.50 in refundable Federal Tax Credits are obtained under Section 6426, if available, along with any other applicable Federal and state credits or incentives.

In yet another embodiment of the invention, application is made to the EPA for registration of esters that meet the definition of Advanced Biofuel or Biomass-based Diesel as appropriate according to the Energy Independence and Security Act of 2007, Section 211. In doing so, these esters will meet the statutory definition of renewable fuel according to the EPA Regulation of Fuels and Fuel Additives: Renewable Fuel Standard Program and these esters will then be assigned a Renewable Identification Number (RIN).

Brief Description of the Drawings

Figure 1 shows one embodiment of the present reaction for the preparation of fatty acid esters via heterogeneous, slurry phase reactive distillation.

Figure 2 shows another embodiment of the present invention for the preparation of fatty acid esters, include a separation step for the ester product.

Figure 3 shows another embodiment of the present invention, further including a pre- esterification process.

Figure 4 shows another embodiment of the present invention, further providing a settling tank.

Figure 5 shows another embodiment of the present invention, further including a reaction vessel for the preparation of a fatty acid ester and ether additive. o

Figure 6 shows another embodiment of the present invention, further including a fat splitter.

Detailed Description

The present invention relates to a method of obtaining U.S. Federal and State tax credits, renewable fuel treatment and other incentives via the production of ester fuels.

Obtaining Tax Credits or Other Production Incentives

In the U.S., federal and state tax credits as well as producer incentive payments can be obtained for the production and sale of "Biodiesel" (also known as biodiesel) hereinafter defined as monoalkyl esters of long chain fatty acids derived from plant or animal matter which meet (A) the registration requirements for fuels and fuel additives established by the Environmental Protection Agency under section 211 of the Clean Air Act (42 U.S. C. 7545), and as amended by the Energy Independence and Security Act of 2007 and (B) the requirements of the American Society of Testing and Materials D6751.

Tax credits for the production of and sale of ester-based fuels are provided under three sections of Internal Revenue Code (IRC) (U.S. Code of Federal Regulations Title 26) . Section 4OA provides non-refundable credits for the use or sale of pure esters meeting the above specifications and registration requirements. IRC Section 4OA provides refundable tax credits for "Biodiesel" of $0.50 per gallon for general biodiesel. Section 4OA also provides refundable credits of $1.00 per gallon for Agri-biodiesel hereinafter defined as biodiesel derived solely from virgin oils, including esters derived from virgin vegetable oils from corn, soybeans, sunflower seeds, cottonseeds, canola, crambe, rapeseeds, safflowers, flaxseeds, rice bran, and mustard seeds, and from animal fats. IRC Section 4OA also provides $0.10 per gallon of small producers credits for qualified small producers of Agri-biodiesel where qualified small producers are defined by the code.

IRC Section 6426 provides refundable credits of $0.50 per gallon for general biodiesel and $1.00 per gallon for Agri-biodiesel mixtures for sale or use in a trade or business of the taxpayer. The term "Biodiesel mixture" is further qualified as:

a mixture of Biodiesel and diesel fuel (as defined in section 4083(a)(3)), determined without regard to any use of kerosene, which

(A) is sold by the taxpayer producing such mixture to any person for use as a fuel, or

(B) is used as a fuel by the taxpayer producing such mixture.

IRC Section 6426 also provides refundable tax credits of $0.50 per gallon for liquid hydrocarbons, other than ethanol, methanol, or biodiesel, derived from biomass that are used as a fuel in a motorboat or motor vehicle. Section 6426 also provides refundable credits of $0.50 per gallon for mixtures of alternative fuels with taxable fuel that are sold or used as fuel by the taxpayer.

Section 211 of the Clean Air Act (42 U.S. C. 7545), as amended by the Energy Independence and Security Act of 2007 provides for the treatment of advanced bio fuels and biomass-based diesel (both considered "biodiesel" for purposes of this document) as a qualifying fuel under the EPA Renewable Fuel Standard Program, and the registration thereof resulting in the creation of renewable identification numbers (RINs) for every 1,000 gallons

produced.

Several state legislatures have also weighed in with various tax credits and other incentives that relate back to the Biodiesel and Alternative Fuel definitions promulgated by IRC, as summarized in Table 1 :

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Depending on the final composition of the product produced according to the methods of the invention, various Federal and State tax credits and other production incentives are available. The procedure for obtaining tax credits under U.S. Code Title 26 section 6426 and 4OA, for example, depends on which components meet Biodiesel, Agri-biodiesel, or Alternative Fuel definitions and specifications. The procedure for obtaining renewable fuel treatment and generating RINs under the EPA Clean Air Act as amended by the Energy Independence and Security Act of 2007 depends on whether the esters meet Biodiesel, Advanced Biofuels or Biomass-based fuels definitions and specifications.

In order to claim Federal tax credits, the claimant must first apply and be approved for "Certain Excise Tax Activities" registration. Once this is accomplished, and depending on whether the claimant will be claiming the tax credit directly or not, certain record-keeping requirements must be met and claims for tax credits filed.

As noted above, the product of the method of the invention can be blended with taxable fuel prior to sale or use under Section 6426. When this is done, the tax credits, if available, are refundable. Alternatively, the product can be used by the tax payer without blending or placed directly in the tank of an end user at retail in order to generate non- refundable credits under Section 4OA.

If the producer qualifies under Section 4OA as a small Agri-Biodiesel producer, then Section 4OA small Agri-Biodiesel producer credits, if available, can be claimed. Production of Ester Fuels

Biodiesel and Agri-Biodiesel fuels consist primarily of esters of fatty acids, particularly methyl esters. Generally, the formation of esters from carboxylic acids, for example, proceeds according to the following reaction:

R¹C(O)OH + R²OH ^^ R¹C(O)OR² + H₂O where R¹ is hydrogen or a monovalent organic radical and R² is a monovalent organic radical. As noted previously, fatty acid esters can also be produced by transesterifϊcation where by glycerides are reacted with alcohols in the presence of acid or base catalysts to yield esters and glycerin. Production of fatty acid esters by transesterifϊcation generally produces a product stream having salts and soaps resulting from treatment with acids and/or bases, and a significant concentration of unreacted glycerin. Esterification of fatty acids according to the present invention allows for the inclusion of glycerin in the feedstock without undue consequence to the resulting product.

Other esters of other carboxylic acids can also be prepared according to the method of the invention. For example, rosin acids from paper making and cellulosic ethanol production can be esterified and then sold as fuel.

The process of the present invention employs the vapor stream of the more volatile of the two components, (i.e. the more volatile out of the fatty acid component and the alcohol component), to carry away water produced in the esterification reactor, while advantageously not carrying away a significant quantity of the less volatile component. For this reason it is essential in one embodiment that the boiling point of the vapor mixture exiting the esterification reactor, or of the highest boiling compound present in that vapor mixture, be significantly lower, at the pressure prevailing in the uppermost stage of the esterification reactor, than the boiling point at that pressure of either of the less volatile one of the two components. The term "significantly lower" shall mean that the boiling point difference shall be at least about 20⁰C, and preferably at least about 25°C, at the relevant operating pressure of the column. In the practice, the more volatile component of the two will frequently be the alcohol component. For example methanol will be the more volatile component in the production from fatty acid mixtures obtained by the hydrolysis of triglycerides of methyl fatty acid ester mixtures for subsequent processing, for example for production of detergent alcohols by ester hydrogenation.

Whereas typical esterifϊcation processes employ pure or nearly pure (i.e., 99% or greater) fatty acid feed stocks, the present invention provides a process wherein the feedstock may comprise at least 2% glycerin, at least 3%, at least 4%, at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, or at least 10% glycerin included in the fatty acid feedstock as a result of the splitting of the triglycerides.

Generally, any source of triglycerides can be used to prepare the fatty acid ester derivatives that provides a fuel additive composition with the desired properties. Suitable fatty acids for esterifϊcation include, but are not limited to, fatty acids such as decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic,acid, octadecanoic acid, octadecenoic acid, linoleic acid, eicosanoic acid, isostearic acid and the like, as well as mixtures of two or more thereof. Mixtures of fatty acids are produced commercially by hydrolysis of naturally occurring triglycerides of vegetable origin, such as coconut oil, rape seed oil, and palm oils, tall oils and triglycerides of animal origin, such as lard, bacon grease, yellow grease, tallow and fish oils. Additional triglycerides may be sourced from whale oil and poultry fat, as well as corn, palm kernel, soybean, olive, sesame, and any other oils of animal or vegetal origin not explicitly identified herein. Other sources of fatty acids include algae (eukaryotic or prokaryotic or mixed), bacteria, and fungi. Other whole plant oils are also suitable. The soaps generated in the refining of tall oil, soybean oil, rapeseed oil, canola oil, and palm oil can also be acidulated by methods known to those skilled in the art to yield fatty acids suitable for esterifϊcation and generation of tax credits under the method of the current invention. In general, while fatty acid esters are preferred for generating the higher level of tax credits, esters of rosin acids can also be utilized according to the present invention.

If desired, mixtures of acids can be subjected to distillation to remove lower boiling acids having a lower boiling point than a chosen temperature (e.g. Cs to C₁₀ acids) and thus produce a "topped" mixture of acids. Optionally, the mixtures can be distilled to remove higher boiling acids having a boiling point higher than a second chosen temperature (e.g. C22+ acids) and thus produce a "tailed" mixture of acids. Additionally, both lower and higher boiling acids may be removed and thus produce a "topped and tailed" mixture of acids. Such fatty acid mixtures may also contain ethylenically unsaturated acids such as oleic acid. These fatty acid mixtures can be esterified with methanol to yield methyl fatty acid ester mixtures.

In another aspect of the present invention, biodiesel fuels prepared according to the present invention are provided. Sulfur content of the biodiesel fuel is one of many parameters of interest for commercial use. Sulfur is typically present as a result of the use of sulfuric acid catalysts, and can result in increased engine wear and deposits. Additionally, environmental concerns dictate a desired low sulfur content in the biodiesel fuel. Preferably, biodiesels prepared according the methods provided herein have a sulfur content (as measured by ASTM test method D5453) of less than 500 ppm, more preferably less than 200 ppm, less than 100 ppm, less than 50 ppm, less than 25 ppm, less than 10 ppm, and most preferably less than 5 ppm.

It is preferred that biodiesel fuels prepared according to the present method have a relatively high flash point, preferably greater than 130⁰C, more preferably greater than 140⁰C, even more preferably greater than 150⁰C, and most preferably greater than 160⁰C. J

The cetane number (i.e., the measure of the ignition quality of the fuel, as measured by ASTM test methods D976 or D4737) is preferably greater than 47, more preferably greater than 50, and most preferably greater than 55.

Cloud points are defined as the temperature at which a cloud or haze of crystals appears in the fuel. Cloud points determine the climate and season in which the biodiesel fuel may be used. Preferably the cloud point of the biodiesel is less than 0⁰C, more preferably less than -5°C, less than -10⁰C, less than -15°C, less than -20⁰C, less than -25°C, less than -30⁰C, less than -35°C, less than -40⁰C, and most preferably, less than -45°C.

Total free glycerin in the biodiesel is preferably less than 0.03% by weight, more preferably less than 0.20% by weight, less than 0.018% by weight, less than 0.016% by weight, and most preferably, less than 0.015% by weight. Total glycerin present in the biodiesel fuel is preferably less than 0.25% by weight, more preferably less than 0.24% by weight, less than 0.23% by weight, less than 0.22% by weight, 0.21% by weight, and most preferably, less than 0.20% by weight.

Residual methanol in the biodiesel is desired to be minimized, and is preferably less than 0.2% by weight, more preferably less than 0.18% by weight, and most preferably less than 0.15% by weight.

Water content in the biodiesel fuel produced according the present invention is preferably less than 500 ppm, preferably less than 450 ppm, more preferably less than 400 ppm and most preferably less than 300 ppm.

It can be important to define a minimum viscosity of the biodiesel fuel because of power loss due to injection pump and injector leakage. Preferably, the viscosity of the biodiesel fuel is between 1.0 and 8.0 mm²/s, more preferably between 1.9 and 6.0 mm²/s, even more preferably between 3.5 and 5.0 mm²/s. Alcohols

A variety of alcohols may be suitable for use in the present etherifϊcation reaction, including any Ci_6 straight, branched, or cyclic alcohols. Preferably, the alcohol is selected from t-butanol or isobutanol, or a mixture thereof.

The alcohols employed are preferably anhydrous, however the presence of a small amount of water is acceptable for the present reaction.

Catalyst

The esterification reaction of the present invention preferably employs a solid heterogeneous catalyst having acidic functional groups on the surface thereof. By heterogeneous is meant that the catalyst is a solid, whereas the reactants are in gaseous and liquid state, respectively.

The solid esterification catalyst may be a granular ion exchange resin containing - SO₃H and/or -COOH groups. Macroreticular resins of this type are preferred. Examples of suitable resins are those sold under the trade marks AMBERLYST, DOWEX, DOW, and PUROLITE such as AMBERLYST 13, AMBERLYST 66, DOW C351 and PUROLITE C150.

The catalyst used on each tray or similar vapor liquid equilibrium affecting device can be a single solid esterification catalyst selected from particulate ion exchange resins having acidic groups. A synthetic zeolite or other type of mixed or singular oxide ceramic material with sufficient acidity could also be employed. Furthermore, different trays or stages could contain different catalyst. In other cases, even when a monocarboxylic acid ester is the desired product, the alcohol component and the carboxylic acid component can be reacted to equilibrium in the presence of an acidic ion exchange resin prior to introduction of the resulting equilibrium mixture to the column reactor. JO

Solid particulate catalyst may also be employed. In this case, the charge of solid particulate or granular esterifϊcation catalyst on each tray is typically sufficient to provide a catalyst: liquid ratio on that tray corresponding to a resin concentration of at least 0.2% w/v, for example a resin concentration in the range of from about 2% w/v to about 20% w/v, preferably 5% w/v to 10% w/v, calculated as dry resin. Sufficient catalyst should be used to enable equilibrium or near equilibrium conditions to be established on the tray within the selected residence time at the relevant operating conditions. Additionally, the amount of catalyst on each tray should be maintained such that agitation by the upflowing vapor is sufficient to prevent "dead spots." For a typical resin catalyst a resin concentration in the range of from about 2% v/v to about 20% v/v, preferably 5% v/v to 10% v/v may be used.

Reaction Vessel

The present invention may be practiced in a variety of reaction vessels, preferably in distillation columns having a variety of catalyst arrangements. Preferably, the vessel includes a reaction zone providing means for sufficiently contacting the reactants in the presence of a catalyst. Such means may include a plurality of trays, or structured packing that operates similar to the trays in a column. A suitable distillation column for reactive distillation according to the present invention is described in U.S. Pat. No. 5,536,856 (Harrison et al.) which is incorporated herein by reference. A different design for the equilibrium stages is described in U.S. Pat. No. 5,831,120 (Watson et al.), and Sulzer sales brochures ("Katapak: Catalysts and Catalyst Supports with Open Crossflow Structure" by Sulzer Chemtech (undated)), each of which is incorporated herein by reference.

Exemplary structured packing preferably includes porous catalyst supports and flow channels for the stripping gas between the catalyst supports. In the flow channels, the downward directed flow of the liquid and the upwardly directed stripping gas contact, in the presence of the acidic solid catalyst, so the esterifϊcation can take place. Preferably, the catalyst is macroporous. Additionally, the catalyst selected must have sufficient stability (i.e., minimal loss of activity) at the operating temperatures necessary, depending upon the alcohol component of the reaction. For example, if methanol, ethanol, n- propanol, isopropanol, n-butanol, tert-butanol or isobutanol is selected as the alcohol, then the catalyst (for example, an ion exchange resin), must be able to be used at temperatures between 120⁰C and 140⁰C; and must only moderately lose activity in this temperature range. If however, 2-ethyl-hexanol is selected as the alcohol component, then the catalyst should be usable at higher temperatures, such as for example, approximately 150° to 230⁰C.

In certain embodiments, the catalyst can be a fixed-bed catalyst. In a fixed bed arrangement, the reaction vessel can be operated as a trickle column of which about 30 to 60 vol%, preferably 50 vol% are utilized by the stripping gas as free gas space, whereas 30 to 50 vol%, preferably 40 vol% of the column is occupied by solid substance, i.e. the fixed-bed catalyst. The remaining reaction space, preferably 10 vol% or less, is occupied by the trickling liquid. When using a fixed bed, the residence time of the liquid phase can be adjusted by the stripping gas velocity. The residence time of the liquid phase is high with higher velocities of the stripping gas volume. Generally, the stripping gas throughput can be adjusted in a wide range without having an adverse effect on the course of process.

Reaction Conditions

The esterification conditions used in a distillation reactor according to the present invention will normally include the use of elevated temperatures up to about 160⁰C. Typically, the reaction conditions are determined based upon the boiling point of the less volatile component, typically the alcohol component. Generally, the esterification reaction may be conducted at a temperature in the range of from about 80⁰C to about 140⁰C, preferably in the range of from about 100⁰C to about 125°C. The particular operating temperature of the reaction is also determined based on the thermal stability of the esterifϊcation catalyst, the kinetics of the reaction and the vapor temperature of the less volatile component at the relevant inlet pressure. Typical operating pressures at the inlet of the column reactor may range from about 0.1 bar to about 25 bar. Additionally, the liquid hourly space velocity through the column reactor may range of from about 0.1 hr^"1 to about 10 hr^"1, typically from about 0.2 hr^"1 to about 2 hr^"1, may be used.

Referring now to Figure 1, there is provided an embodiment of a process for the esterifϊcation of fatty acid feed stock having between 1-10% glycerin. A fatty acid feedstock 1 is supplied to column 5 via line 2. If the fatty acid is the less volatile component (compared to the alcohol), then fatty acid 1 is supplied to the upper portion of the column, preferable above a reaction zone 6. An alcohol 3, preferably methanol, is supplied to the column via line 4. If the alcohol is the more volatile component (compared with the fatty acid), then the alcohol 3 is supplied to the bottom of column 5, preferably below the reaction zone 6.

The reaction zone 6 preferably includes trays or structured packing which includes a heterogeneous catalyst, preferably an ion exchange resin having acidic functional groups. If structured packing is employed, preferably achieving the same vapor-liquid contact as is accomplished with trays. One of skill in the art can determine the equivalent size and type of packing for a given number of trays in a distillation column.

The alcohol is introduced at the bottom of the column as a vapor, traveling upward through the trays, and preferably contacting the fatty acid in the reaction zone in the presence of the appropriate esterifϊcation catalyst. Column 5 preferably includes means for heating the alcohol to produce a vapor stream. The alcohol stream exits column 5 via line 7, preferably including at least a portion of the water produced by the esterifϊcation reaction.

The alcohol stream can be supplied to an alcohol/water separation unit 8, which separates the stream into a water-rich stream 12 and an alcohol rich stream 9, which can be recycled to the distillation column 5. Product stream 10 exits the distillation column as the bottoms liquid, and includes fatty acid alkyl ethers and glycerin. The bottoms stream 10 may also include mono-, di- and tri-alkyl ethers of glycerin.

Referring now to Figure 2, an alternate embodiment of the process shown in Figure 1 is presented. Figure 2 shows the process of Figure 1, and further employs a means for separating 11 the product stream 10. The means can be any means known in the art for the separation of glycerin and unreacted fatty acids from the product esters, such as for example, using a settling tank, distillation, reboiled stripping, inert gas stripping, or physical adsorption. The separation means 11 results in a ester-rich stream 13 and a glycerin or fatty acid containing stream 14.

Referring to Figure 3, the embodiment according to Figure 2 is provided, further including a pre-esterifϊcation unit 16, to which the glycerin/fatty acid feed stock is introduced via line 15. The use of a pre-esterifϊcation unit is known in the art, such as is described in U.S. Pat. No. 5,536,856 (Harrison et al.) and incorporated herein by reference.

Referring now to Figure 4, the embodiment according to Figure 1 is provided, further including means for separating glycerin and the fatty acid ester product of line 13. Accordingly, the product mixture is supplied to a settling tank 17 via line 13. The contents of the tank are allowed to settle, and the fatty acid esters 18 may be separated from the glycerin 19.

Referring now to Figure 5, an alternate embodiment of the process according to Figure 1 is provided, further including means for producing a biodiesel feed which includes glycerin ether additives. The glycerin ether additives are produced by reacting glycerin with an alcohol in the at a proper temperature and pressure, in the presence of a catalyst, to produce a mixture of mono-, di- and tri-ethers of glycerin. Crude fatty acid ester product stream 10, which may contain glycerin and unreacted fatty acids, is introduced to a second reaction vessel 20. Reaction vessel 20 is preferably a distillation column configured for reactive distillation. The crude fatty acid ester product stream 10 is introduced into the distillation column above a reaction zone 20. Reaction zone 20 preferably includes trays (equilibrium stages) which include an etherification catalyst. Suitable catalyst for the etherification includes those previously identified as esterification catalysts.

An alcohol 22, preferably tert-butanol, isobutanol or isoamyl alcohol, can be introduced as a vapor to the bottom of reaction vessel 20 via line 23, and functions similar to the alcohol vapor employed in the esterification reactor.

The alcohol vapor 22 reacts with the glycerin from crude feed 10 to produce glycerin ethers. Vaporous alcohol and water resulting from the etherification reaction exit the reactor via line 24, and is introduced to separator 25. Separator 25 may be any known means for separating water from methanol, such as for example, a distillation column. An alcohol rich stream 26 is supplied form separator 25 to the bottom of the etherification reactor 20 as a vapor. Water exits the separator 25 via line 27.

Product stream 28 exits the reaction vessel 20 as a bottoms stream, preferably including the fatty acid ester product of reaction vessel 5 and a glycerin alkyl ether additive.

Referring now to Figure 6, an alternate embodiment for the production of biodiesel fuels is provided. Triglycerides from animal or vegetal oils are supplied via line 29 to a fat splitting unit employing steam to separate triglycerides into component fatty acids and glycerol. The fat splitting unit is known in the art, such as is provided in U.S. Pat. No. 2,486,630 (Brown), incorporated herein by reference. The majority of the glycerin is separated from the fatty acids, and removed from the fatty acid feedstock via line 31. The fatty acid stream from the fat splitter 30 is supplied to the upper portion of the reactive distillation column, preferable above a reaction zone 6. An alcohol 3, preferably methanol, is supplied to the column via line 4.

The alcohol is introduced at the bottom of the column as a vapor, traveling upward through the trays, and preferably contacting the fatty acid in the reaction zone in the presence of the appropriate esterification catalyst. Column 5 preferably includes means for heating the alcohol to produce a vapor stream. The alcohol stream exits column 5 via line 7, preferably including at least a portion of the water produced by the esterification reaction.

The alcohol stream can be supplied to an alcohol/water separation unit 8, which separates the stream into a water-rich stream 12 and an alcohol rich stream 9, which can be recycled to the distillation column 5.

Product stream 10 exits the distillation column as the bottoms liquid, and includes fatty acid alkyl ethers and glycerin. The bottoms stream 10 may also include mono-, di- and tri-alkyl ethers of glycerin.

The product stream 10 is supplied to a separation means 11 to remover impurities from product stream 10. The separation means can be any means known in the art for the separation of glycerin and unreacted fatty acids from the product esters, such as for example, using a settling tank for gravity separation. Optionally, the separation means may also include a filter bed (not shown) which includes bauxite, clay or ion exchange resin beads for further purification. The separation means 11 results in a ester-rich stream 13 and a glycerin or fatty acid containing stream 14. It will be understood by those skilled in the art that the drawings are diagrammatic and that further items of equipment such as reflux drums, pumps, vacuum pumps, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks, and the like may be required in a commercial plant. The provision of such ancillary items of equipment is in accordance with conventional chemical engineering practice. Modifications and variations of the present invention relating to the selection of fatty acid feedstocks, alcohols and catalysts are intended to come within the scope of the invention. All references cited herein are hereby incorporated by reference.

Claims

1. A method for obtaining U.S. Federal tax credits under Title 26 Sections 4OA and/or 6426 for ester based fuels, and/or a method for obtaining Renewable Identification Numbers under the EPA Clean Air Act as amended by the Energy Independence and Security Act of 2007, comprising:

(A) passing one or more carboxylic acid components and an alcohol component countercurrently through an esterification zone maintained under esterification conditions and containing a solid esterification catalyst selected from particulate ion exchange resins having sulphonic acid groups, carboxylic acid groups or both, wherein

(i) the esterification zone comprises a column reactor provided with a plurality of esterification trays mounted one above another, each adapted to hold a predetermined liquid volume and a charge of particles of a solid esterification catalyst thereon, liquid downcomer means associated with each esterification tray adapted to allow liquid phase to pass down the column reactor from each esterification tray but to retain the particles of solid esterification catalyst thereon, and vapor upcomer means associated with each esterification tray adapted to allow vapor to enter each esterification tray from below and to agitate and maintain the suspension of the mixture of liquid and solid esterification catalyst on that esterification tray, each esterification tray having a floor that slopes towards a zone of turbulence under said vapor upcomer means to prevent formation of stagnant zones of particles of catalyst thereon; and

(ii) the less volatile component of the carboxylic acid component and of the alcohol component is supplied in liquid phase to an upper part of the column reactor above the uppermost esterification tray, while the more volatile component of the carboxylic acid component and of the alcohol component is supplied in vapor form beneath the lowermost one of said plurality of esterification trays; and (iii) vapor comprising said more volatile component and water of esterifϊcation is recovered from an upper part of the column reactor; and

(iv) wherein said carboxylic acid ester is recovered from a lower part of the column reactor;

(B) selling or using as fuel the carboxylic acid ester of step (A)(iv) with or without blending said carboxylic acid ester with taxable fuel; and

(C) having a tax payer use the product of step (B) as a basis for a claim for U.S. Federal tax credits under Title 26 Sections 4OA and/or 6426, and/or for U.S. Federal Renewable Identification Numbers under Environmental Protection Agency Clean Air Act as amended by the Energy Independence and Security Act of 2007.

2. A method according to claim 1, wherein the more volatile component is the alcohol component and the less volatile component is the one or more carboxylic acid components.

3. A method according to claim 1, wherein the alcohol component is an alkanol containing from 1 to about 10 carbon atoms.

4. A method according to claim 3, wherein the alkanol is methanol.

5. A method according to claim 3, wherein the water content of the alkanol vapor supplied to the column reactor is less than about 5 mole %.

6. A method according to claim 1, wherein the carboxylic acid component is an aliphatic monocarboxylic acid or a mixture thereof.

7. A method according to claim 6, wherein the carboxylic acid component is a mixture of fatty acids.

8. A method according to claim 1, wherein the carboxylic acid component contains a mixture of rosin acids.

9. A method according to claim 1, wherein the column reactor is operated at a temperature of from about 8O⁰C to about 14O⁰C and at a pressure of from about 1 bar to about 25 bar.

10. A method according to claim 1, wherein the carboxylic acid ester recovered from a lower part of the column reactor is admixed with additional alcohol component and is passed through a fixed bed of a solid esterification catalyst.

11. The method of claim 1 , wherein the carboxylic acids are derived from hydrolysis of mono-, di-, or tri-glycerides.

12. The method of claim 1, wherein the carboxylic acids are distilled from a mixture of fatty acids and glycerides.

13. The method of claim 1, wherein the carboxylic acids are produced by the acidulation of soy, palm, canola, rapeseed, jahtropa, or vegetable oil soapstock.

14. The method of claim 1, wherein the carboxylic acids are produced by the acidulation and fractionation of tall oil soaps.

15. The method of claim 1, wherein the carboxylic acids are derived from hydrolysis and distillation of mixtures of fatty acids and triglycerides.